Identifying N fertilizer regime and vegetable production system in tropical Brazil using 15N natural abundance

BACKGROUND This study was conducted in areas of vegetable production in tropical Brazil, with the objectives of (i) measuring the variation in δ15 N in soils, organic N fertilizer sources and lettuce (Lactuca sativa L.) from different farming systems, (ii) measuring whether plant δ15 N can differentiate organic versus conventional lettuce and (iii) identifying the factors affecting lettuce δ15 N. RESULTS Samples of soil, lettuce and organic inputs were taken from two organic, one conventional and one hydroponic farm. The two organic farms had different N-sources with δ15 N values ranging from 0.0 to +14.9‰ (e.g. leguminous green manure and animal manure compost, respectively), and differed significantly (P < 0.05) in lettuce δ15 N (+9.2 ± 1.1‰ and +14.3 ± 1.0‰). Conventional lettuce δ15 N (+8.5 ± 2.7‰) differed from hydroponic lettuce δ15 N (+4.5 ± 0.2‰) due to manure inputs. The N from leguminous green manure made a small contribution to the N nutrition of lettuce in the multi-N-source organic farm. CONCLUSION To differentiate organic versus conventional farms using δ15 N the several subsets of mode of fertilization should be considered. Comparisons of δ15 N of soil, organic inputs and lettuce allowed a qualitative analysis of the relative importance of different N inputs. © 2015 Society of Chemical Industry